Mrs Hudson must step into action once more. It's summer in London, and things are quiet. But while Sherlock Holmes and Dr. Watson chafe at their inactivity, a train carrying a vital secret is entering a tunnel in an obscure region of the Balkans - never to be seen again. The train is only the beginning. The missing message must be found and decoded, and a diplomat's wife must be rescued from the clutches of a pernicious blackmailer. The...